With regard to some strollers with reversible seat in the market, the stroller frame can only be collapsed after the reversible seat is removed. With regard to some other strollers with reversible seat in the market, the stroller frame can only be collapsed when the reversible seat is mounted in a given orientation. If the stroller frame is collapsed when the reversible seat is mounted in a different orientation, the reversible seat will significantly protrude outside the stroller frame and thus will not be snugly collapsed along with the stroller frame, resulting in the inconvenience for the use's collapsing of the stroller frame, the inconvenience for carrying and storage, and the annoyance for the parents.